Insulating joint for cable sheaths



May 27, 1930. E. D. EBY 1,760,546

INSULATING JOINT FOR CABLE SHEATHS Filed Feb. 25, 1927 Inventor: Eugene D. 13b3, b M His Attorneg.

Patented May 27, 1930 UNITED STATES PATENT OFFICE EUGENE D. EBY, OF PITTSFIELD, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A. CORPORATION OF NEW YORK INSULATING JOINT FOR CABLE SHEATHS Application filed February 25, 1927.

In the operation of underground cables, especially those carrying high tension electric currents, it is necessary to interrupt the electrical continuity of the lead covering or sheath at suitable intervals by means of insulating joints, to prevent the building up of excessive induced voltage in said sheath. Owing to the fact that these joints have to be applied in manholes where the conditions are such as to make all kinds of work extremely difficult, it is important that the joints be of such a character that they can be completed in the factory and shipped to the point of installation. The problem of making a satisfactory joint is further complicated when used for oil-filled cables, as in the present instance, by the fact that in addition to insulating thesections of the sheath from each other, the joints must be fluid-tight.

The object of my invention is to provide an improved form of insulating joint for cable sheaths which is simple in construction, is capable of successfully insulating the cable sections, is capable of withstanding substantial fluid pressure without leaking, and which can be made as a unit in the factory thereby avoiding much hand work at the point of installation.

For a consideration of what I believe to be novel and my invention, attention is directed to the accompanying description and the claims appended thereto.

In the attached drawing, Fig. 1 is a partial longitudinal section of a high tension oil-filled cable and Fig. 2 shows a slight r, modification in the way the insulating joint is applied.

3 indicates a cable of any desired construction wherein one or more conductors are pro vided and Wrapped with suitable insulation 4 such as paper tape. Surrounding the insulation is a lead sheath 5, the continuity of which is interrupted at suitable intervals. Within the cable oil is maintained under suitable pressure. The arrangements for accomplishing this latter are not material in the present instance as they may be of any well-known construction.

6 ind cates a y dr al bo y of insu at- Serial No. 170,990.

ing material which may be molded or turned to shape, and which should be impervious to the oil used as an insulating medium in the cable. A material well adapted for the purpose is composed of bakelite-treated canvas in which the latter is held under compression by the former. The sides of the body are parallel to each other and perpendicular to the axis of the cable. In the periphery of the body is a rather deep groove, which has the effect of forming a rib at each end of the body and all of the exterior surfaces are well rounded to prevent cracking of the metal parts seated thereon as Well as of the insulator itself.

At each side of the body is a compressible gasket 7. The body is retained in a twopiece metallic holder 8, the inner faces or parts of which are spaced apart as at 9 to prevent the flow of current from one part to the other. These parts are made of spun metal, usually copper, and each comprises a cylindrical portion '10 which surrounds the sheath and when installed is connected thereto by a wiped soldered joint 11. Extending perpendicularly to the portion 10 is a flange 12 which forms a shoulder or wall upon which is seated the gasket 7. In forming these flanged parts they are partially spun to shape as roughly indicated by the dotted lines 13, after which the body 6 and the two metallic members are mounted in a fixture under suitable end ressure and the spinning completed, the ody 6 serving as a former. This spinning of the metal over the rounded ribs of the body to form inturned ends has the eflect of compressing gaskets 7 by a sufficient amount to make fluid-tight joints at each side of the body. When the spinning has been completed the two parts of the holder are firmly united through the medium of the body or bridge member and thereafter can be treated as a unit and shipped to the point of installation.

The procedure for installing the joints will now be described, it being assumed that the cable has been laid in the conduits. and the adjacent ends of two sections are located in a manhole. Having cut the cable ends to the required dimensions the insulating joint slipped over one of them to a position beyond its point of application. The jointer then cuts away a portion of the lead sheath, the portion removed being approximately equal in axial length to' that of the insulating body 6. The cutting operation slightly raises the edges of the lead sheath from the insulation 4.

In a high tension cable it is important to prevent the concentration of electric stresses at any one point or points as would be occasioned by the presence of any relatively sharp corners or projecting or rough metal points where the sheath is cut. This concentration is avoided in the following manner:

Into the space formed between the lead and the paper one edge of a thin copper or other metallic element or band 14 is slipped, said band covering a little more than half of the length of the cable from which the lead sheath has been removed. The band may with advantage be in the form of a slotted cylinder with the edges of the joints in abutting relation. After being inserted the lead is hammered down on the band as smoothly as possible. Over this is wound a body of cambric or other tape 15 which also covers a small portion of the paper or factory wound insulation 4:. A second band 16, also of thin copper and similarly constructed, is slipped into the space between the lead sheath and the paper insulation and is made to lie flat on the paper and on the tape 15 by any suitablemeans as by hammering the end of the sheath and also the tape itself. Over the band is then wound cambric or other tape 17 the diameter of which when completed is slightly less than the diameter of the bore of the metal casing of the joint. The jointer then slips the joint endwise until it is in the position shown, after which the cylindrical ends of the holder are soldered to the sheath by wiped joints. The grooved portion of the joint is covered with asphaltum or other tape 18 which serves as an additional means to make the joint fluidtight. 1 This tape may be applied before or after the joint is shipped from the factory.

The joint thus described is separate from the cable joint or splice. In some cases it will be found advantageous to combine the two in one structure. Such an arrangement is shown in Fig. 2. The details of the joint itself are the same but the arrangement for supporting it are different. As is well understood, these splicing joints are provided with casings and I utilize these to support the insulating joints, there being one such joint for each casing. In this figure 20 indicates the casing of the splicing joint one side of which is made in two parts 21 and 22 and between said parts is interposed the body of insulation 6, the parts of the casing being spun over the side portions of the body in the same manner as previously described. In order to mount the casing in place on the cable it must be made in separable parts as is well-understood, usually by dividing it into two parts, the joint being perpendicular to the axis of the cable. Due to the fact that the insulating body 6 is securely held by the inturned ends of the enclosing metal members, it will be seen that the element containing the insulating joint can be treated as a unit just as though it were made wholly of metal.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An insulating joint for cable sheaths comprising a pair of tubular members having outer ends which are secured fiuid-t1ght to the parts of the sheath and facing enlarged ends which are spaced apart, and a cylindrical body located between the spaced ends which insulates the members and has external ribs which are gripped by the en larged ends of the members.

2. An insulating joint for cable sheaths comprising a pair of spaced tubular members having outer ends which are secured to the parts of the sheath and facing ends which have gripping flanges with inturned ends, a cylindrical body of insulating material situated between said flanges and through which the body of the cable extends, the ends of said body having projections which enter and are retained by the gripping action of the flanges, and means situated between the body and flanges which are held under compression thereby.

3. In combination, a cable having an interrupted sheath, a pair of tubular metal members which are secured at their outer ends to separated portions of the sheath and have flanged facing ends, a body of insulating material located between the flanged ends and through which the cable extends, said body having end enlargements which are gripped by said flanged ends, and means for preventing the concentration of electrical stresses in the region of the interrupted portion of the sheath.

4. As an article of manufacture an insulating joint for the sheaths of electric cables comprising a pair of tubular members arranged end to end and which have opposed flanges with inturned edges, a hollow body of insulating material which is situated between said flanges and has ribs which are enclosed and gripped by the inturned edges, and gaskets which are located between the flanges and the ends of the hollow body and are held under compression by the gripping action of flanges on said ribs.

5. As an article of manufacture an insulating joint for the sheaths of electric cables comprising a pair of tubular members, the outer ends of which are adapted to snugly fit the parts of the cable sheath, the inner ends having flanges which form seats and also inturned grippin ed es, a hollow body of lnsulation throng w ich the cable is adapted to extend, the periphery of said body having ribs on each side thereof, the ribs being situated between said seats and grip- Bing edges and securely held in place there- 6. As an article of manufacture an insulating joint for the sheaths of electric cables comprising a pair of tubular members, the outer ends of which are adapted to snugly fit the parts of the cable sheath, the inner ends having flanges which form seats and also inturned gripping ed es, a hollow body of insulation through w ich the cable is adapted to extend, the periphery of said body having a central roove with ribs on each side thereof, the ribs in situated between said seats and gripping e ges and securely held in place thereby and means impervious to moisture which fill in the roove and cover the adjacent edges of the anges.

In witness whereof, I have hereunto set my hand this 21st da of February, 1927 UGENE D. EBY. 

